Safety-paper.



UNITED STATES PATENT OFFICE.

ERNEST EMIL SCHMIDT, OF COVINGTON, KENTUCKY.

SAFETY-PAPER.

No Drawing.

To all whom it may concern:

Be it known that I, ERNEST EMIL SCHMIDT, a citizen of the United States, residing at Covington, in the county of Kenton and State of Kentucky, have invented new and useful Improvements in Safety- Paper, of which the following is a specification.

This invention relates to paper used for checks, notes, wills, deeds, etc., and has for its ob ect to prevent successful fraudulent alteration of matter written on such paper with commercial fluid writing ink.

For this purpose I impregnate the paper, or the pulp from which it is made, with an agent adapted to chemically combine with the essential ingredients of commercial writ ing ink in rendering matter written with said ink indelible either by the acid and alkaline solutions usually employed to remove commercial ink from paper, or by the abrasive action of a mechanical eraser.

I have used with satisfactory results an agent composed of a solution of ferrdcyanid of potassium, or its chemical equivalent, viz., ferro-cyanid of sodium, or; gall, magnesium sulfate, and water, using by preference the following proportions:

Ferro-cyanid of potassium (or ferrocyanid of sodium), two pounds,

Ox gall, three ounces,

Magnesium sulfate, one ounce,

Water, four gallons.

Any ordinary writing paper impregnated with said solution becomes very sensitive to commercial writing inks, all of which contain tannate of iron or other similar preparation of iron, in quantity suflicient to make the written matter legible, and also contain nut gall and tannin. The ink a t once combines with the said agent and is rendered practically indelible, so that it cannot be successfully removed without detection, either by means of chemical ink eradicators or by mechanical abrasion.

In eradicating commercial -writing ink. two liquid solutions are applied successively or alternately to the paper, one being acid and, the other alkaline. Either of said 2-'()llltions alone is not capable of removing' the ink without leaving evidence of fraud, but

the two solutions used successively are capable of entirely removing any commercial ink from ordinary paper.

Specification 01' Letters Patent.

the desired tint or color.

Patented Feb. 20, 1917.

Application filed January 26, 1916. Serial No. 74,500.

When paper treated in accordance with my invention has been Written upon with any ink and an attempt is made to remove cating the ink, the acid immediatelysetsthe ink by combining with the iron and tannin of the ink and with the'ferro-cyanid of potassium (or sodium) in the paper, forming ferro-cyanid of'iron, which is insoluble in all acids and alkalis, and is therefore indelible, and cannot be removed without destruction of the paper. 7

If an alkali is first used, it will similarly set the ink and render it indelible.

In either case the chemicalaction is such that evidence of fraud is plainly visible on the paper.

The ex gall incorporated in the paper has the effect of causing fluid ink to penetrate or sink into the paper to such an extent as to materially increase the difficulty of successfully removing the ink from the paper by a mechanical eraser or other abrading instrumentality.

The magnesium sulfate hardens the paper and prevents the ink from creeping laterally at the surface of the paper, and thus blurring the written lines.

To further guard against fraud, I provide the paper with coloring matter, preferably by adding anilin dye to the solution above described, in sufficient quantity to impart The anilin dye combines with any ink-cradieating chemical that may be applied to the paper, the result being a strongly contrasting color wherever the eradicator touches the paper, entirely defeating the fraudulent ntent.

The dye may be applied only to the external surface of the paper, so that the color of the surface contrasts with that of the body of the paper. Mechanical erasure therefore removes the surface color and ex poses a patch of contrasting color. If now an attempt is made to again color the ex posed patch, any coloring matter used will so combine with the chemical agent in the paper as to produce a different color from a... Manama, .i i in.

If White paper is specified equivalent, ox gall, and magnesium sulfate.

6. Safety paper impregnated with a solution of ferro-cyanid of potassium or its specified equivalent, ox gall, and magnesium 2 sulfate, the paper being treated with color; ing matter which is changeable by acid and alkaline ink eradicators.

7. Safety paper impregnated with a s0- lution of ferro-cyanid of potassium or its 25 specified equivalent, ox gall, magnesium sulfate, and anilin coloring matter.

In testimony whereof I have aflixed my signature.

ERNEST EMIL SCHMIDT. 

